1. Field of the Invention
This invention relates generally to heat exchangers for refrigerant circuits and, more particularly, to the heat medium conducting elements which constitute a heat exchanging area of the heat exchangers.
2. Description of the Prior Art
Various types of heat exchangers are known in the prior art. For example, U.S. Pat. No. 5,211,222 to Shinmura discloses a laminated type heat exchanger used for an evaporator of an automotive air conditioning refrigerant circuit, as shown in FIG. 1-3. With reference to FIGS. 1-3, the laminated type evaporator 200' includes a plurality of tube units 201 of aluminum alloy functioning as the heat medium conducting elements, which form a heat exchanging area 200a of evaporator 200' together with corrugated fins 20. Each of tube units 201 comprises a pair of tray-shaped plates 202 having a clad construction where a brazing metal sheet is formed on a core metal.
As illustrated in FIGS. 2 and 3, each of tray-shaped plates 202 includes a shallow depression 120 defined therein, a flange 13 formed around the periphery thereof, and a narrow wall 14 formed in the central region thereof. Narrow wall 14 extends downwardly from an upper end of plate 202 and terminates approximately one-seventh the length of plate 202 away from the lower end thereof. Narrow wall 14 includes a flat top surface 14a. A plurality of diagonally disposed semicylindrical projections 15 project from the inner bottom surface of shallow depression 120. Semicylindrical projections 15 are aligned with one another in each of a plurality of, for example, four rows. There are two rows of semicylindrical projections 15 located in shallow depression 120 on the right side of narrow wall 14 and two rows located on the left side thereof. Semicylindrical projections 15 include a ridge 15a and are utilized in order to reinforce the mechanical strength of plate 202.
Each of tray-shaped plates 202 includes a pair of tapered connecting tongues 203 projecting upwardly from the upper end thereof. One of the tongues 203 is disposed to the right of narrow wall 14, and the other tongue 203 is disposed to the left thereof. A depression 203a is formed in the central region of tongue 203, longitudinally extends from the upper end to the lower end thereof, and is linked to shallow depression 120 of plate 202. The bottom surface of depression 203a is formed even with the plane of the inner bottom surface of shallow depression 120. A pair of diagonally disposed semicylindrical projections 204 are formed on the bottom surface of depression 203a. Semicylindrical projections 204 also include a ridge 204a and are utilized in order to reinforce the mechanical strength of tongues 203. Semicylindrical projections 204 are longitudinally aligned with each other and are offset from the two rows of semicylindrical projections 15 formed on the inner bottom surface of shallow depression 120.
The edges of flat top surface 14a of narrow wall 14, the flat top end surface of each of tongues 203, ridge 15a of semicylindrical projections 15 and ridge 204a of semicylindrical projections 204 are even with the plane of flange 13. Therefore, when the pair of tray-shaped plates 202 are joined together by flanges 13 so as to form a U-shaped passage 205 therebetween, the pair of tongues 203 of the pair of plates 202 define a pair of tapered hollow connecting portions 203b, narrow walls 14 of each plate 202 contact one another at the flat top surfaces 14a, semicylindrical projections 15 of plates 202 contact one another at ridges 15a, and semicylindrical projections 204 of tongues 203 contact one another at ridges 204a. Flanges 13 of plates 202, the flat top end surface of each of tongues 203, the flat top surfaces 14a of narrow walls 14 in plates 202, semicylindrical projections 15 of plates 202 and semicylindrical projections 204 of tongues 203 are fixedly attached to each other by brazing, or a like manner.
Laminated type evaporator 200' further includes a pair of parallel closed ended cylindrical pipes 230 and 240 situated above the upper surface of laminated tube units 201. As illustrated in FIG. 2, cylindrical pipe 230 is positioned in front of cylindrical pipe 240. A plurality of generally oval-shaped slots 231 are formed along the lower curved surface of cylindrical pipe 230 at equal intervals. A plurality of generally oval-shaped slots 241 are also formed along the lower curved surface of cylindrical pipe 240 at equal intervals. Generally, oval-shaped slots 231 of pipe 230 are aligned with generally oval-shaped slots 241 of pipe 240 so as to receive the pair of tapered hollow connecting portions 203b of tube units 201. The pair of tapered hollow connecting portions 203b of tube units 201 are inserted into slots 231 and 241 until the lower end portion of connecting portions 203b contacts the inner peripheral surface of slots 231 and 241, respectively. The pair of tapered hollow connecting portions 203b are fixedly attached to slots 231 and 241, respectively by, for example, brazing.
A pair of circular openings 232 and 233 (FIG. 1) are formed at the left and right ends of cylindrical pipe 230, respectively, on the front curved surface thereof. One end of inlet pipe 50 is fixedly connected to opening 232 of cylindrical pipe 230 and one end of outlet pipe 60 is fixedly connected to opening 233 of cylindrical pipe 230. Inlet pipe 50 is provided with a union joint 50a at the other end thereof and outlet pipe 60 is similarly provided with a union joint 60a at the other end thereof.
Circular plate 234 is fixedly disposed at an intermediate location within the interior region of cylindrical pipe 230 so as to divide the cylindrical pipe 230 into a left side section 230a and a right side section 230b, as shown in FIG. 1.
A rectangular flange 18 projects from the lower end of plate 202, and is bent downwardly in a generally right angle at the terminal end thereof. The downwardly bent portion of adjacent flanges 18 are attached to each other so that an intervening space 21 is formed between the adjacent tube units 201.
The heat exchanging area 200a of evaporator 200' is formed by laminating together a plurality of tube units 201 and inserting corrugated fins 20 within the intervening spaces 21 between the adjacent tube units 201. A pair of side plates 22 are attached to the left side of plate 202a which is located on the far left side of evaporator 200' and the right side of plate 202b which is located on the far right side of evaporator 200', respectively, and corrugated fins 20 are disposed between side plate 22 and plate 202a, and between side plate 22 and plate 202b, respectively. The lower end of side plate 22 includes a rectangular flange 22a projecting inwardly and then bent downwardly in a generally right angle at the terminal end thereof. Respective tube units 201, corrugated fins 20, and side plates 22 are fixedly attached to one another by any conventional manner, such as brazing, for example. Although corrugated fins 20 are only illustrated in FIG. 1 at the upper and lower ends of intervening spaces 21, it should be understood that corrugated fins 20 continually extend along the entire length of intervening spaces 21.
In the above-constructed evaporator 200', when the automotive air conditioning refrigerant circuit operates, the refrigerant flows from a condenser (not shown) of the refrigerant circuit via a throttling device, such as an expansion valve, through inlet pipe 50 into left side section 230a of the interior region of cylindrical pipe 230, and through left side section 230a in a left to right direction. The refrigerant flowing through left side section 230a of the interior region of pipe 230 concurrently flows through the interior region of tapered hollow connecting portions 203b and into the upper right region of U-shaped passage 205 in each of tube units 201. The refrigerant in the upper right region of U-shaped passage 205 then flows downwardly to the lower right region of passageway U-shaped 205 in a complex flow path, which includes diagonal and straight flow paths as shown by the solid arrows in FIG. 3, while also exchanging heat with the air passing along corrugated fins 20. The refrigerant located in the lower right region of U-shaped passage 205 is turned at the terminal end of narrow wall 14 and directed from the right side to the left side of U-shaped passage 205, as shown by the solid arrows in FIG. 3. That is, the refrigerant flows from the front to the rear of U-shaped passage 205, then flows upwardly to the upper left region of U-shaped passage 205 in a complex flow path while further exchanging heat with the air passing along corrugated fins 20, and then finally flows out of U-shaped passage 205 in each of tube units 201 through tapered hollow connecting portion 203b. The refrigerant flowing out of U-shaped passage 205 from each of tube units 201 combines in the interior region of cylindrical pipe 240 and flows therethrough in a direction from the left side to the right side thereof.
The refrigerant flowing through the interior region of the right side of cylindrical pipe 240 concurrently flows into the upper left region of U-shaped passage 205 in each of tube units 201 through tapered hollow connecting portion 203b, and flows downwardly to the lower left region of U-shaped passage 205 in a complex flow path and exchanges heat with the air passing along corrugated fins 20. The refrigerant located in the lower left region of U-shaped passage 205 is turned at the terminal end of narrow wall 14 and directed from the left side to the right side of U-shaped passage 205. That is, the refrigerant flows from the rear to the front of U-shaped passage 205, then flows upwardly to the upper right region of U-shaped passage 205 in a complex flow path while further exchanging heat with the air passing along corrugated fins 20, and finally flows out of U-shaped passage 205 from each of tube units 201 through tapered hollow connecting portions 203b. The refrigerant flowing from U-shaped passage 205 in each of tube units 201 combines in the right side section 230b of the interior region of cylindrical pipe 230 and flows therethrough in a direction from the left side to the right side thereof. The gaseous phase refrigerant located in the far right side of right side section 230b in the interior of cylindrical pipe 230 flows through outlet pipe 60 to the suction chamber of a compressor (not shown) in the refrigerant circuit.
In the manufacturing process of evaporator 200', pairs of plates 202 are fixedly joined to each other by means of brazing the mating surfaces, e.g., the plane of flanges 13, the flat top end surfaces of tongues 203, the flat top surfaces 14a of narrow walls 14, the intersecting points of ridges 15a of semicylindrical projections 15 and the intersecting points of ridges 204a of semicylindrical projections 204, to one another, in general, in an inert gas, such as a helium gas atmosphere. In general, before the pair of plates 202 are fixedly joined to each other by brazing, aluminum oxide formed on the surfaces to be mated must be removed in order to effectively and sufficiently braze the pair of plates 202. For example, the surfaces to be mated are treated with flux so as to remove the aluminum oxide formed thereon.
According to one method of treating the pair of plates 202 with flux, the flux is dissolved in the water and sprayed on the mating surfaces of the pair of plates 202. However, in this treatment method, the flux solution cannot be selectively sprayed only on the mating surfaces. Rather, the flux solution is additionally sprayed on the other, nonmating portions of the pair of plates 202, such as, the inner bottom surface of shallow depression 120 and the bottom surface of depression 203a. Consequently, residual flux remains on the inner bottom surface of shallow depression 120 and the bottom surface of depression 203a after the pair of plates 202 are brazed to one another.
The residual flux has been observed to peel off throughout the life of the heat exchanger. The flakes of residual flux then circulate through the refrigerant circuit during operation of the automotive air conditioning system. The circulating flakes of residual flux flowing through the refrigerant circuit may choke the refrigerant flow path of the refrigerant circuit so that the automotive air conditioning system may be seriously damaged and/or the heat exchange efficiency is impaired.
In order to avoid the above-mentioned defect, a "vacuum brazing process", where the elements of the evaporator are brazed in a vacuum, has been proposed. However, the vacuum brazing process requires a relatively large space for the vacuum pump, and elaborate and frequent maintenance for assuring the appropriate amount of vacuum in the brazing furnace.
These and other disadvantages of the prior art are addressed by the heat exchanger of the preferred embodiments.